Project Summary/Abstract Although the naturally occurring peroxide artemisinin has played a major role in the fight against malaria, the difficulty of synthesizing peroxides has made it challenging for medicinal chemists to pursue many types of peroxides as drug candidates. The long-term objective of this research program is to develop new methods for the synthesis of peroxides and to explore their biological activity. Preliminary experiments indicate that metal- catalyzed reactions of O2 provide new methods to prepare peroxides, that these reactions can occur with regio- and stereoselectivity, and that five-membered ring peroxides are selectively active against cancer cells. The cause of cell death elicited by these compounds is not apoptosis, the common pathway induced by anti- cancer drugs, suggesting that the atypical peroxide structure leads to atypical activity. The following specific aims will be pursued: (1) we will develop new methods for stereoselective peroxidation using O2; (2) we will explore new approaches for the one-step synthesis of cyclic peroxides; and (3) we will develop methods for the stereoselective synthesis of five-membered ring peroxides and evaluate their biological activity. In the first Aim, we will extend preliminary studies indicating that metal-catalyzed reactions of O2 can be used to introduce the peroxide functional group stereoselectively into organic compounds, including furans, and that those compounds can be transformed into structures resembling natural products. The second Aim will examine new methods for the one-step incorporation of O2 into organic compounds for the synthesis of cyclic peroxides, a family of compounds that exhibits diverse and potent biological activity. The third Aim will refine our understanding of how five-membered ring peroxides cause cell death by ferroptosis, an iron-dependent form of cell death discovered by Professor Brent Stockwell (Columbia University). These studies will be performed in collaboration with Professor Stockwell and with Professor William Carroll (NYU Perlmutter Cancer Center) and Professor Lara Mahal (NYU Department of Chemistry). We will also evaluate new methods for the stereoselective synthesis of these peroxides because we have demonstrated that the biological activity depends upon stereochemistry. The proposed research is innovative because it uses new metal-catalyzed reactions to introduce the peroxide functional group, and because it attempts to solve selectivity issues that are not well addressed in the literature. The proposed research is significant because it will lead to new reactions and methods for the synthesis of a challenging functional group that is part of compounds with potent biological activity. The biological studies will be significant because they will provide insight into ferroptosis. These studies are relevant to human health because the mechanism of action by which five-membered ring peroxides kill cancer cells is distinct from the pathways followed by most drugs, suggesting that peroxides could serve as complementary treatments for cancers that are unresponsive to many chemotherapy agents.